A source of sound emits sound waves at frequency $f _ { 0 }$. It is moving towards an observer with fixed speed $v _ { s } \left( v _ { s } < v \right)$, where $v$ is the speed of sound in air. If the observer were to move towards the source with speed $v _ { 0 }$, one of the following two graphs (A and B) will give the correct variation of the frequency $f$ heard by the observer as $v _ { 0 }$ is changed. The variation of $f$ with $v _ { 0 }$ is given correctly by: (1) Graph A with slope $= \frac { f _ { 0 } } { \left( v - v _ { s } \right) }$ (2) Graph A with slope $= \frac { f _ { 0 } } { \left( v + v _ { s } \right) }$ (3) Graph B with slope $= \frac { f _ { 0 } } { \left( v - v _ { s } \right) }$ (4) Graph B with slope $= \frac { f _ { 0 } } { \left( v + v _ { s } \right) }$
A source of sound emits sound waves at frequency $f _ { 0 }$. It is moving towards an observer with fixed speed $v _ { s } \left( v _ { s } < v \right)$, where $v$ is the speed of sound in air. If the observer were to move towards the source with speed $v _ { 0 }$, one of the following two graphs (A and B) will give the correct variation of the frequency $f$ heard by the observer as $v _ { 0 }$ is changed.
The variation of $f$ with $v _ { 0 }$ is given correctly by:\\
(1) Graph A with slope $= \frac { f _ { 0 } } { \left( v - v _ { s } \right) }$\\
(2) Graph A with slope $= \frac { f _ { 0 } } { \left( v + v _ { s } \right) }$\\
(3) Graph B with slope $= \frac { f _ { 0 } } { \left( v - v _ { s } \right) }$\\
(4) Graph B with slope $= \frac { f _ { 0 } } { \left( v + v _ { s } \right) }$